iOS: How can Objective C code read static variables in Swift?

Question

For Example, say if I have a class like so with a static variable pi.

let pi: Double = 3.1415926

 class MyClass {
// ...
 }

How can I allow Objective C code to use the static variable pi? The projectName-Swift.h class will have auto generated code like so (just a small example and not 100 percent accurate).

  SWIFT_CLASS("_MyClass")
 @interface MyClass : NSObject
 - (instancetype)init OBJC_DESIGNATED_INITIALIZER;
 @end

So pi isn't being added to projectName-Swift.h. This is a small example on what is going on with my project and perhaps it should generate the static variable and I am missing something. Any tips or suggestions to fix this or make this work will be appreciated.

Can you use a class method to expose the static variables for your use case? — JRG-Developer, Mar 11 '15 at 17:30
I will have to modify the Objective c code, but I guess it could work just fine. Also, you mean something like this? class var pi : Double { return 3.1415926 } — William Alex, Mar 11 '15 at 17:34
You should take a look at http://stackoverflow.com/questions/25918628/how-to-define-static-constant-in-a-class-in-swift This goes down the path suggested by JRG, especially Martin's answer — Peter M, Mar 11 '15 at 18:11

score 29 · Answer 1 · edited May 23 '17 at 12:09

29

You can't access Swift global variables on Objective C.

You’ll have access to anything within a class or protocol that’s marked with the @objc attribute as long as it’s compatible with Objective-C. This excludes Swift-only features such as those listed here:

Generics

Tuples

Enumerations defined in Swift

Structures defined in Swift

Top-level functions defined in Swift

Global variables defined in Swift

Typealiases defined in Swift

Swift-style variadics

Nested types

Curried functions

Using Swift with Cocoa and Objective-C

Check this post too.

edited May 23 '17 at 12:09

Community

1
1

answered Apr 27 '15 at 17:35

eduardoeof

399
2
6

1

(xCode 7.3.1) Looks like that `@objc` is not needed anymore. Also, a root class can't be accessed from Objective-C, you have to inherit `NSObject` – Axel Guilmin Aug 29 '16 at 15:48

score 1 · Answer 2 · answered Jun 09 '21 at 06:32

1

You also need to indicate that they are public

@objc public class MyClass { 
    @objc public static let pi = 3.14
}

answered Jun 09 '21 at 06:32

Booharin

753
10
10

score 0 · Answer 3 · answered Apr 22 '21 at 18:52

0

I would make pi static and put it inside MyClass. Also add @objc infront of each of them like this.

@objc class MyClass { 
    @objc static let pi = 3.14
}

Then in your objective C code you can call it like this

CGFloat piValue = MyClass.pi;

answered Apr 22 '21 at 18:52

candyline

788
8
17

iOS: How can Objective C code read static variables in Swift?

3 Answers3